Single channel full duplex wireless communication

ABSTRACT

A single channel full duplex wireless communication system includes a processor, a transmitter, a receiver, a secondary transmission path, a combining element, a primary transmission feedback path and a secondary transmission feedback path. The transmitter transmits a transmission signal via a transmission path. The receiver receives a received signal via a reception path. The transmitter and the receiver utilize one channel to transmit and receive signals. The transmission signal causes self-interference. The processor estimates a first transfer function and feeds the secondary transmission path with the transmission signal adjusted by the first transfer function to reduce the transmission signal leaked to the reception path. The combining element combines the transmission signal with the adjusted secondary transmission path signal to remove the self-interference. The primary transmission feedback path output is modified by a second transfer function. The secondary transmission feedback path output is modified by a third transfer function.

CROSS REFERENCE TO RELATED APPLICATIONS

The application claims priority to U.S. Provisional Application No.61/570,357, filed Dec. 14, 2011, the contents of which are incorporatedentirely herein by reference.

FIELD OF THE INVENTION

The present invention relates to duplex wireless communication, and moreparticularly, to systems and methods providing single channel fullduplex wireless communication.

BACKGROUND OF THE INVENTION

Duplex communication systems are methods of transmitting signals thatallow two people or two parts to communicate with one another inopposite directions. Duplex communication systems are widely used in thearea of telecommunications and especially in telephony and computernetworking Existing duplex wireless communication systems includehalf-duplex and full duplex types.

Existing half-duplex wireless communication systems provide forcommunication in two directions, but only in one direction at a time.Thus, while the transmitter is transmitting, the receiver must waituntil the transmitter stops before transmitting. Such systems requiresignificant latency periods.

Full-duplex (also known as double-duplex) systems are capable oftransmitting and receiving data-carrying signals simultaneously. Suchsystems still require that the transmissions be separated in some way toenable the receivers to receive signals at the same time astransmissions are being made. Such separation may be achieved by twowell-known methods: frequency separation using frequency division duplex(FDD) and time separation using time division duplex (TDD).

FDD systems include a transmission antenna and a reception antenna andoperate using two independent, non-overlapping channels, one fortransmitting and one for receiving. This method requires implementationof complex filters to separate the very weak received signal from thevery strong transmission signal and to enable the receiver not to beunduly affected by the transmitter signal.

TDD systems are capable of transmitting in two directions, but use asingle channel that alternates between transmitting and receiving. Thusthe transmitter and receiver operate on the same frequency, but only inone direction at a time. TDD systems do not require two channels andfrequency selective filters to separate the received signal from thetransmission system. However, TDD systems require a guard interval thatincludes (1) the time required for the transmission to travel from thetransmitter to the receiver and (2) the time required for the receiverto change from receive to transmit mode. Thus, TDD systems tend tointroduce more overhead and more latency than protocols used withfull-duplex operations and are not generally suitable for use over longdistances.

Frequency spectrum is becoming an increasingly scarce resource, whiletechnological progress, particularly in the area of 3G and 4Gtelecommunication systems and wireless internet services, has greatlyincreased the demand for wireless broadband. Both full-duplex andhalf-duplex wireless communication systems utilize the wirelesschannel(s) in only one direction at any given moment of time, thereforewasting spectrum. There is a growing need to optimize the use ofavailable spectrum and to provide a method and apparatus that canachieve satisfactory performance for short, medium, and long distancecommunications and allows a full-duplex wireless system to operate on asingle channel, i.e., to utilize the wireless channel in both directionsat the same time, therefore doubling the spectral efficiency.

Different solutions have been proposed to solve this problem. However,these solutions either involve the use of extra components such asantennas or other processing components, which means added complexityand cost.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a system for improvingsignal-to-interference ratio in a single channel full duplex wirelesscommunication apparatus by significantly reducing self-interference ispresented.

One embodiment of the present invention provides a method for improvingsignal-to-interference ratio in a single channel full duplex wirelesscommunication apparatus by significantly reducing self-interference.

One embodiment of the present invention relates to a system thatincludes a processor, a transmitter coupled to the processor, a receivercoupled to the processor, a secondary transmission path coupled to thetransmitter, a combining element coupled to the receiver, a primarytransmission feedback path and a secondary transmission feedback path.The transmitter transmits a transmission signal via a transmission path.The receiver processes a received signal via a reception path. Thetransmitter and the receiver utilize one channel, at the same time, totransmit and receive the transmission and received signals. Thetransmission signal causes self-interference. The processor estimates afirst transfer function and feeds the secondary transmission path withthe transmission signal adjusted by the first transfer function in sucha way that the secondary transmission path signal reduces thetransmission signal leaked to the reception path. The combining elementis configured to combine the transmission signal with the adjustedsecondary transmission path signal, thereby removing at least a fractionof the self-interference.

According to a further aspect of the present invention, the primarytransmission feedback path output is modified by a second transferfunction. The secondary transmission feedback path output is modified bya third transfer function, such that combining of the modified primarytransmission feedback path output and the modified secondarytransmission feedback path output to the reception path output reducesthe remaining fraction of the self-interference.

Another aspect of the present invention relates to a method of improvingsignal-to-interference ratio in a single channel full duplex wirelesscommunication system. The method includes transmitting a transmissionsignal via a transmission path. The method also includes receiving areceived signal via a reception path. The transmission path and thereception path utilize one channel, at the same time, to transmit andreceive transmission and received signals. The transmission signalcauses self-interference. The processor estimates a first transferfunction. The processor feeds a secondary transmission path with thetransmission signal adjusted by the first transfer function in such away that the secondary transmission path signal reduces the transmissionsignal leaked to the reception path, thereby removing at least afraction of the self-interference. The secondary transmission path iscoupled to the transmitter. A combining element coupled to the receivercombines the transmission signal with the adjusted secondarytransmission path signal.

According to a further aspect of the present invention, the processoralso estimates a second transfer function and a third transfer function.The processor modifies a primary transmission feedback path outputsignal with the second transfer function and a secondary transmissionfeedback path output signal with the third transfer function. Theprocessor adds the modified primary transmission feedback path outputand the modified secondary transmission feedback path output to thereception path output, thereby canceling the remaining fraction of theself-interference.

Yet another aspect of the present invention relates to a single channelfull duplex wireless communication system including a processor, atransmitter coupled to the processor, a receiver coupled to theprocessor. The transmitter transmits a transmission signal via atransmission path. A portion of the transmission signal is leaked. Thereceiver receives a received signal. The received signal includesleakage from the transmission signal. The receiver includes at least onecombining element and at least one reception path. The at least onecombining element is coupled to an input of the receiver. At least onereception path is coupled to an output of the receiver. The receiverproduces an output signal, the output signal including self-interferencecaused by the leakage from the transmission signal. The system alsoincludes a secondary transmission path coupled to the transmitter and tothe combining element. The processor is configured to estimate a firsttransfer function and to feed the secondary transmission path with atleast a portion of the transmission signal adjusted by the firsttransfer function to produce a first intermediate signal at an output ofthe secondary transmission path. A first cancellation signal is obtainedbased upon the first intermediate signal. The first cancellation signalis subsequently combined with the received signal in the at least onecombining element so as to reduce the self-interference in the outputsignal from the receiver. A second cancellation signal is generated bymodifying a second intermediate signal using a second transfer function.The second transfer function is estimated by the processor. The secondintermediate signal is obtained based on at least one of thetransmission signal and the first intermediate signal. The secondcancellation signal is subsequently combined with the output signal fromthe receiver within the processor, thereby further reducing theself-interference in the output signal from the receiver.

A further aspect of the present invention relates to a method ofreducing self-interference caused by one or more transmission signals ina single channel full duplex wireless communication apparatus. Themethod includes transmitting one or more transmission signals using atransmitter, the transmitting occurring via one or more transmissionpaths coupled to the transmitter. One or more portions of the one ormore transmission signals are leaked. The method includes receiving oneor more received signals using a receiver, the one or more receivedsignals including leakage from the one or more transmission signals. Thereceiver includes one or more combining elements and one or morereception paths. At least one combining element is coupled to an inputof the receiver. The receiver produces one or more output signals. Theone or more output signals include(s) self-interference, theself-interference being caused by the leakage from the one or moretransmission signals. The method also includes generating one or morefirst cancellation signals. The generating of one or more firstcancellation signals further includes estimating, by a processor, afirst transfer function, feeding, by the processor, one or moresecondary transmission paths with one or more portions of the one ormore transmission signals adjusted by the first transfer function toproduce one or more first intermediate signals at output(s) of the oneor more secondary transmission paths, each one of the one or moresecondary transmission paths being coupled to the transmitter and to theone or more combining elements of the receiver. The generating of one ormore first cancellation signals further includes obtaining the one ormore first cancellation signals from the one or more first intermediatesignals and combining, using the one or more combining elements withinthe receiver, the one or more received signals with the one or morefirst cancellation signals in the one or more combining elements of thereceiver, thereby reducing the self-interference in the one or moreoutput signals. The method also includes generating one or more secondcancellation signals. The generating of one or more second cancellationsignals further includes estimating a second transfer function, thesecond transfer function being estimated by a processor and generatingone or more second intermediate signals, the second intermediate signalsbeing generated by obtaining portions of the one or more transmissionsignals. The generating of one or more second cancellation signals alsoincludes using one or more secondary transmission feedback path outputsignals, wherein inputs to the one or more secondary transmissionfeedback paths are coupled to the outputs of the one or more secondarytransmission paths and modifying the one or more second intermediatesignals with the second transfer function to obtain the one or moresecond cancellation signals. The method also includes combining, in theprocessor, the one or more second cancellation signals with the one ormore output signals from the receiver, thereby further reducing theself-interference in the one or more output signals.

One embodiment provides a method for improving signal-to-interferenceratio in a single channel full duplex wireless communication apparatusover short, medium, and long-distances.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the following descriptionof preferred embodiments together with reference to the accompanyingdrawings, in which:

FIG. 1 is an embodiment of a single channel full duplex wirelesscommunication system.

FIG. 2 is another embodiment of a single channel full duplex wirelesscommunication.

FIG. 3 is another embodiment of a single channel full duplex wirelesscommunication system.

FIG. 4 is another embodiment of a single channel full duplex wirelesscommunication system.

FIG. 5 is another embodiment of a single channel full duplex wirelesscommunication system.

FIG. 6 is another embodiment of a single channel full duplex wirelesscommunication system.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

Although the invention will be described in connection with certainpreferred embodiments, it will be understood that the invention is notlimited to those particular embodiments. On the contrary, the inventionis intended to cover all alternatives, modifications, and equivalentarrangements as may be included within the spirit and scope of theinvention as defined by the appended claims.

Turning now to the drawings, FIGS. 1-6 show different embodiments of asingle channel full duplex wireless communication system that isconfigured to operate at a wide range of frequencies and to providesufficient cancellation such that the system may be employed for short,medium, and long-distance wireless communications. FIG. 1 shows anembodiment of a single channel full duplex wireless communication systemincluding a baseband processor 400, a transmission path 420, atransmission splitter 415, a transmission feedback path 410, a receptionpath 440, a combining element 465, a secondary transmission path 460, asecondary transmission splitter 455, a secondary transmission feedbackpath 450, and a circulator-like device 480 that connects thetransmission path 420 via the transmission splitter 415; and thereception path 440 via the combining element 465; to the antenna 490. Areceiver 421 includes the combining element 465 and the reception path440. The input to the receiver 421 is port 482 which in FIG. 1 is alsoan output port of a circulator-like device 480.

The transmission path 420 and the reception path 440 communicate in boththe transmission and the reception direction, while using the samechannel at the same time, unlike half-duplex and full-duplex systemsdescribed above. The circulator-like device 480 that connects thetransmission path 420 and the reception path 440 to the antenna 490 is acirculator or an equivalent device or circuit that is configured toallow the signal entering the circulator-like device 480 through port481 to exit through port 483 with minimal attenuation (less thanapproximately 1 dB) and with only a minor part of signal energy exitingthrough port 482 (approximately 1% of total transmission signal energyor 20 dB). Moreover, the circulator-like device 480 is furtherconfigured to allow the signal entering the circulator-like device 480through port 483 to exit through port 482 with minimal attenuation.

The transmission splitter 415 is a directional coupler or similar devicethat takes a fraction of transmitted signal power at the output of thetransmission path 420 and feeds it to the transmission feedback path410, while feeding most of the transmitted signal power to the port 481.The secondary transmission splitter 455 is a directional coupler,splitter or similar device that feeds a fraction of the signal power atthe output of the secondary transmission path 460 to the secondarytransmission feedback path 450 and another fraction of the power of thesame signal to the combining element 465. The combining element 465 maybe a combiner or a similar device that is capable of combining thesignal from port 482 with the signal from the secondary transmissionsplitter 455 and feeding the resulting combined signal to the receptionpath 440.

The main challenge in a full-duplex communication system and especiallyin a single channel full duplex system is the self-interference, i.e.,the interference caused by the transmission signal on the receivedsignal. Signal strength diminishes quickly over distance; thus thestrength of the received signal is much weaker than that of thetransmission signal. Simultaneously decoding the weak signal whiletransmitting the strong transmission signal has been a challenge.Particularly, sufficient attenuation of the noise associated with theself-interference has been a major obstacle to implementation of singlechannel full duplex systems.

The circulator-like device 480 that connects the transmitter 422 andreceiver 421 to the antenna via the transmission splitter 415 and thecombining element 465 respectively provides some isolation between thetransmitter 422 and the receiver 421, but the isolation is notsufficient to achieve decent/acceptable receiver performance. Since thesame channel is used for the transmission and reception direction, thereis no frequency separation between the operation of the transmitter andthe receiver. This prevents the use of frequency selective filtering,such as FDD systems that are used in existing full-duplex wirelesscommunication systems to enhance the isolation between the transmissionpath 420 and reception path 440. Some transmission signal strength getsreflected at the interface between the circulator-like device 480 andthe antenna 490, or over the air. There is no known device such as thecirculator-like device 480 that would be capable of properly attenuatingthese reflections of the transmission signal.

A practical circulator-like device 480 is generally capable of offeringisolation in the range of 20 dB for an implementation using passivecomponents or 50 dB for an implementation using passive and activecomponents (e.g., active interference canceling techniques). Activetechniques generally differ from passive techniques at least in thatactive techniques utilize a powered source. Assuming the transmissionsignal is 20 dBm, the power of the leaked transmission signal at theinput of the receiver 421 (port 482) would be around 0 dBm or −30 dBm,respectively. If the received signal is −90 dBm, thesignal-to-interference ratio caused by self-interference would be −90 dBor −60 dB, respectively. Thus, signal-to-interference ratio would be notonly negative, but it would also be such that the leaked transmittedsignal (the one causing self-interference) would cause distortion in thereception path 440 to a level that nothing could be done in the basebandprocessor to recover the received signal with an acceptablesignal-to-interference ratio.

For the receiver 421 to operate properly it is necessary to provide amethod for reducing the power of the transmitted signal leaked to theinput of the receiver 421 (port 482) to a level that does not causedistortions in the reception path 440, and to provide a method tofurther improve the signal-to-interference ratio in the basebandprocessor 400.

To reduce the power of the transmitted signal leaked to the input of thereceiver (port 482), the baseband processor 400 feeds a secondarytransmission path 460 with a signal adjusted in such a way that itcancels the transmission signal leaked to the port 482. To do this, thebaseband processor 400:

(1) estimates the transfer function H_(Tx)(x) from the input of thetransmission path 420 to the input of the reception path 440;

(2) estimates the transfer function H_(Sx)(x) from the input of thesecondary transmission path 460 to the input of the reception path 440;

(3) then calculates the transfer function H_(D)(x) 401 that has theproperty that H_(Sx)(H_(D)(x))+H_(Tx)(x)=0. The processor 400 thenpasses the signal at the input of the transmission path 420 through theH_(D)(x) transfer function 401 and applies it to the input of thesecondary transmission path 460 to cancel or reduce the transmissionsignal leaked to the port 482.

If all transfer functions are linear thenH_(Sx)(H_(D)(x))=H_(Sx)(x)·H_(D)(x)) and H_(D)(x) can be computed asH_(D)(x)=−H_(Tx)(x)/H_(Sx)(x). Further to this, if transfer functionsare represented in the analog-domain the variable x is commonly denotedas s and if represented in digital-domain variable x is commonly denotedas z. Most practical implementations will use digital-domainrepresentation of transfer functions. However, the invention is neitherlimited to digital-domain representation nor to linear transferfunctions.

In one embodiment, the baseband processor 400 measures the transferfunction H_(TxRx)(x)=H_(Rx)(H_(Tx)(x)) from the input of thetransmission path 420 to the output of the reception path 440 and thetransfer function H_(SxRx)(x)=H_(Rx)(H_(Sx)(x)) from the input of thesecondary transmission path 460 to the output of the reception path 440,where H_(Rx)(x) is the transfer function of the reception path 440,i.e., from the input of the reception path 440 to its output. Thebaseband processor 400 will calculate the transfer function H_(D)(x) 401for which H_(SxRx)(H_(D)(x))+H_(TxRx)(x)=0. This guarantees thatH_(Sx)(H_(D)(x))+H_(Tx)(x)=0 at least for the frequencies of interest,i.e. frequencies for which H_(Rx)(x) is not null.

In one embodiment, each of the H_(TxRx)(x) and H_(SxRx)(x) is estimatedusing an adaptive filter. An adaptive filter is adjusted to estimate thetransfer function that, when applied to given input signal produces anoutput that resembles a given desired output signal with a minimumerror. For H_(TxRx)(x) the input of the adaptive filter is the input ofthe transmission path 420 and the desired output is the output of thereception path 440. For H_(SxRx)(x) the input of the adaptive filter isthe input of the secondary transmission path 460 and the desired outputis the output of the reception path 440. Once H_(TxRx)(x) andH_(SxRx)(x) are estimated, H_(D)(x) can then be computed using wellknown mathematical algorithms. In case of linear transfer function,H_(D)(x) =−H_(TxRx)(_(x))/Hs_(SxRx)(x).

For linear transfer functions, the most common adaptive filters areWiener and the Least Mean Square (LMS) filter. In both cases, thetransfer functions are adapted by adjusting filter coefficients tominimize the mean square error (MSE) between the desired output and theactual output of the filter when applied to the supplied input. The maindifference between Wiener and LMS filters is how the coefficients areadapted. With the Wiener filter, the filter coefficients are adaptedonly once. More precisely, the input and desired output statistical datais first collected and then the filter coefficients are calculated fromthe collected data. With LMS filter, the filter coefficients are adaptedafter every data sample is taken.

In practical implementations it may be required to use non-lineartransfer functions, at the very least for H_(TxRx)(x) and H_(D)(x), ifnot also for H_(SxRx)(x) . This is especially true when the transmissionpath is operated closer to its maximum transmission power case in whichit introduces non-linear distortions which in turn creates in-bandintermodulation products. One solution is to extend the Wiener or LMSfilter to allow implementation of non-linear transfer functions. Indigital domain both the Wiener and the LMS filters are Finite ImpulseResponse (FIR) filters. The output of an FIR is a weighted sum of termsthat are derived from the input signal by adding delays:v(n)=h ₀ ·u(n)+h₁ ·u(n−1)+h ₂ ·u(n−2)+. . .where u(n) is the input, v(n) is the output and H(z)=h₀+h₁·z⁻¹+h₂·z⁻² +.. . is the filter transfer function whose coefficients h₀, h₁, h₂, . . .are adapted. The nonlinear extension of an FIR is a weighted sum ofterms that are derived from the input signal by adding delays andapplying a Taylor series expansion. In the most general form, thenonlinear filter is:v(n)=h ₁₀ ·u(n)+h ₁₁ ·u(n−1)+h ₁₂ ·u(n−2)+ . . . +h ₂₀₀ ·u(n)² +h ₂₁₁·u(n−1)² +h ₂₂₂ ·u(n−2)²+ . . . +2·h ₂₀₁ ·u(n)·u(n−1)+2·h ₂₀₂·u(n)·u(n−2)+2·h ₂₁₂ ·u(n−1)·u(n−2)+ . . . +h ₃₀₀₀ ·u(n)³ +h ₃₁₁₁·u(n−1)³ +h ₃₂₂₂ ·u(n−2)³+ . . . +3·h ₃₀₀₁ ·u(n)² ·u(n−1)+ . . .and the coefficients can be adapted using the same algorithms as thoseused for the Wiener or LMS filters in the linear case. In most practicalscenarios there is no need to include all higher order terms. Forcommunications systems where the bandwidth is significantly smaller thanthe center frequency, the even order intermodulation products arelocated outside of the bandwidth of existing circuits and are filteredout, which means there is no need to include even powers in the filterterms. Furthermore, power decreases with the order of theintermodulation products. For example, the 5^(th) order intermodulationproducts have much lower power that the 3^(rd) order intermodulationproducts and may not need cancellation. Then, in order to perform thenecessary processing, only 1^(st) and 3^(rd) power terms are considered,that is:v(n)=h ₁₀ ·u(n)+h ₁₁ ·u(n−1)+h ₁₂ ·u(n−2)+ . . . +h ₃₀₀₀ ·u(n)³ +h ₃₁₁₁·u(n−1)³ +h ₃₂₂₂ ·u(n−2)³+ . . . +3·h ₃₀₀₁ ·u(n)² ·u(n−1)+. . .

Due to limited precision, noise, and various imperfections, thesecondary transmission path 460 is generally not adapted to provide adesired amount of cancellation. The transmission path 460 can typicallyimprove signal-to-interference ratio by an amount in the range of 60 dB,which is generally not sufficient to provide a satisfactorysignal-to-interference ratio. Thus, in one embodiment, the basebandprocessor 400 is further adapted to provide additional cancellation.

In the preferred embodiment, the baseband processor 400 uses thetransmission feedback path 410 and the secondary transmission feedbackpath 450 to acquire the signals at the output of the transmission path420 and the secondary transmission path 460 (including the noise, thelinear and the non-linear distortions). The baseband processor 400 thenestimates the transfer functions H_(TF)(x) 402 and H_(TF)(x) 403 thatneed to be applied to the signal at the outputs of the transmissionfeedback path 410 and the secondary transmission feedback path 450,respectively, so that, when added to the received signal present at theoutput of the reception path 440, the remaining self-interference iscompletely cancelled or significantly reduced. In one embodiment theH_(TF)(x) and H_(TF)(x) are adaptive filters with the desired outputbeing the output of the reception path multiplied by −1. In other words,they will adapt to subtract any transmit signal, noise and distortionleft after the cancelation done at the input to the reception path. Inanother embodiment one of the adaptive filters H_(TF)(x) and H_(TF)(x)is trained with the desired output being the output of the receptionpath multiplied by −1 while the other is trained with the desired outputbeing the result of adding the output of the other filter to the outputof the reception path, everything multiplied by −1. In other words, inthe embodiment the two cancelers are cascaded instead of working inparallel.

FIG. 2 shows an embodiment of a single channel full duplex wirelesscommunication system, where a transmission antenna 491 is connected, viathe transmission splitter 415, to the transmission path 420, and areceiver antenna 492 is connected, via the combining element 465, to thereception path 440. The receiver 421 still comprises combining element465 and reception path 440, and the input to the receiver is port 482.The crosstalk between the two antennas, transmitter antenna 491 andreceiver antenna 492, plus the over-the-air reflections causetransmission signal to leak into the input of the receiver (port 482).In other words, the signal received by the combining element 465 fromthe receiver antenna 492 experiences self-interference due to the leakedtransmission signal. Such self-interference needs to be cancelled orreduced in order to achieve desired wireless system performance.

The transmission signal leak is addressed by the processor 400estimating and applying a transfer function H_(D)(x) 401 that has theproperty that H_(Sx)(H_(D)(x))+H_(Tx)(x)=0. The processor 400 thenpasses the signal at the input of the transmission path 420 through thetransfer function H_(D)(x) 401 and applies it to the input of thesecondary transmission path 460 to cancel or significantly reduce thetransmission signal leaked into the input of the receiver (the port 482)at the input of the reception path 440.

Moreover, this embodiment also provides additional cancellation in thebaseband processor 400 via transmission feedback path 410 and thesecondary transmission feedback path 450 as described above in relationto FIG. 1.

FIG. 3 shows an embodiment of a single channel full duplex wirelesscommunication system where the secondary transmission feedback path 420of FIG. 1 is not used and the secondary transmission path 460 isconnected to the combining element 465. This solution is adapted forsystems where the noise of the secondary transmission path 460 is lowenough that cancellation in baseband processor 400 is not required. FIG.5 is a variation of the embodiment shown in FIG. 3 in which thetransmission path 420 is connected, via the transmissions splitter 415,to the transmission antenna 491 and the reception path 440 is connected,via the combining element 465, to the receiver antenna 492. In both FIG.3 and FIG. 5, the input to the receiver 421 is port 482, which is alsoan output port of a circulator-like device 480.

FIG. 4 shows an embodiment of a single channel full duplex wirelesscommunication system where the secondary transmission path 460 isconnected directly to the combining element 465 and where thetransmission path 420 is connected directly to the circulator-likedevice 480. Both the transmission feedback path 410 and secondarytransmission feedback path 450 of FIG. 1 are not used. This solution isadapted for systems where the noise of both the transmission path 420and the secondary transmission path 460 is low enough that cancellationin baseband processor 400 is not required. FIG. 6 is a variation of theembodiment shown in FIG. 4 in which the transmission path 420 isdirectly connected to the transmission antenna 491 and the receptionpath 440 is connected, via the combining element 465, to the receiverantenna 492.

Other embodiments of single channel full frequency communication systemscan be provided, containing multiple secondary transmission paths 460,some of them containing their own splitters 455 and secondary feedbackpaths 450, feeding via different combining elements 465 into differentstages of the reception path 440, wherein the transmission path 420 isconnected to the port 481 of the circulator-like device 480 and thereception path 440 is connected, via one of the combining elements 465to port 482, which as previously explained is both an input port to thereceiver, and an output port of the circulator-like device 480. Everystage achieves removal of additional undesired signal leaked from thetransmission path 420. This method can offer much better removal ofundesired signal leaked from the transmission path 420.

Another embodiment of single channel full frequency communicationsystems can be provided, containing multiple secondary transmissionpaths 460, some of them containing their own splitters 455 and feedbackpaths 450, feeding via different combining elements 465 into differentstages of the reception path 440, wherein the transmission path 420 isconnected to the transmission antenna 491 and the reception path 440 isconnected, via one of the combining elements 465, to the receiverantenna 492. Every stage achieves removal of additional undesired signalleaked from the transmission path 420. This method can offersignificantly better removal of undesired signal leaked from thetransmission path 420.

Another embodiment of single channel full frequency communicationsystems containing multiple-input and multiple-output (MIMO) may beprovided wherein there are multiple transmission paths 420 and multiplereception paths 440. There will be, for example M reception paths 440and N transmission paths 420. There will be M secondary transmissionpaths 460, one for each reception path 440. Such an arrangement cansignificantly improve communication performance. Specifically, inwireless communications, it offers significant increases in datatransmission and link range without using any additional spectrum ortransmit power. It achieves this by higher spectral efficiency and linkreliability. There will be N transmission feedback paths 410 and Msecondary transmission feedback paths 450. The baseband processor 400feeds each secondary transmission path 460 with the necessary signal tocancel or reduce the interference from each transmission path 420 to therespective reception path 440. The baseband processor 400 supplies thesignals at the input of the M secondary transmission paths 460 throughan M×N matrix of transfer functions H_(D)(s) 401. In other words, eachof the M inputs will be the sum of N transmitted signals processedthrough N distinct transfer functions.

Similarly, there will a matrix of M×N H_(TF)(x) 402 transfer functionsand a matrix of M×M H_(SF)(x) 403 transfer functions that need to beapplied to the signal at the outputs of the transmission feedback path410 and the secondary transmission feedback path 450, respectively, sothat, when added to the received signal present at the output of thereception path 440, the remaining self-interference is completelycancelled.

The embodiments described above are implemented in a variety of ways.Generally, the embodiments described above may be implemented usinghardware, software or a combination of hardware and software elements.The hardware aspects may include combinations of operatively coupledhardware components including microprocessors, logical circuitry,communication/networking ports, digital filters, memory, or logicalcircuitry. The hardware may be adapted to perform operations specifiedby a computer-executable code, which may be stored on a computerreadable medium.

The baseband processor 400 described above may be implemented in avariety of ways, using, for example, an external conventional computeror an on-board field programmable gate array (FPGA) or digital signalprocessor (DSP), that executes software, or stored instructions. Thebaseband processor 400 may be implemented using one or more networked ornon-networked general purpose computer systems, microprocessors, fieldprogrammable gate arrays (FPGAs), digital signal processors (DSPs),micro-controllers, and the like, programmed according to the teachingsof the exemplary embodiments of the present invention, as is appreciatedby those skilled in the computer and software arts.

The steps of the methods described herein may be achieved via anappropriate programmable processing device, such as an externalconventional computer or an on-board field programmable gate array(FPGA) or digital signal processor (DSP), that executes software, orstored instructions. In general, physical processors and/or machinesemployed by embodiments of the present invention for any processing orevaluation may include one or more networked or non-networked generalpurpose computer systems, microprocessors, field programmable gatearrays (FPGAs), digital signal processors (DSPs), micro-controllers, andthe like, programmed according to the teachings of the exemplaryembodiments of the present invention, as is appreciated by those skilledin the computer and software arts. Appropriate software can be readilyprepared by programmers of ordinary skill based on the teachings of theexemplary embodiments, as is appreciated by those skilled in thesoftware arts. In addition, the devices and subsystems of the exemplaryembodiments can be implemented by the preparation ofapplication-specific integrated circuits or by interconnecting anappropriate network of conventional component circuits, as isappreciated by those skilled in the electrical arts. Thus, the exemplaryembodiments are not limited to any specific combination of hardwarecircuitry and/or software.

Stored on any one or on a combination of computer readable media, theexemplary embodiments of the present invention may include software forcontrolling the devices and subsystems of the exemplary embodiments, fordriving the devices and subsystems of the exemplary embodiments, forprocessing data and signals, for enabling the devices and subsystems ofthe exemplary embodiments to interact with a human user, and the like.Such software can include, but is not limited to, device drivers,firmware, operating systems, development tools, applications software,and the like. Such computer readable media further can include thecomputer program product of an embodiment of the present invention forperforming all or a portion (if processing is distributed) of theprocessing performed in implementations. Computer code devices of theexemplary embodiments of the present invention can include any suitableinterpretable or executable code mechanism, including but not limited toscripts, interpretable programs, dynamic link libraries (DLLs), Javaclasses and applets, complete executable programs, and the like.Moreover, parts of the processing of the exemplary embodiments of thepresent invention can be distributed for better performance,reliability, cost, and the like.

Common forms of computer-readable media may include, for example, afloppy disk, a flexible disk, hard disk, magnetic tape, any othersuitable magnetic medium, a CD-ROM, CDRW, DVD, any other suitableoptical medium, punch cards, paper tape, optical mark sheets, any othersuitable physical medium with patterns of holes or other opticallyrecognizable indicia, a RAM, a PROM, an EPROM, a FLASH-EPROM, any othersuitable memory chip or cartridge, a carrier wave or any other suitablemedium from which a computer can read.

While particular embodiments and applications of the present inventionhave been illustrated and described, it is to be understood that theinvention is not limited to the precise construction and compositionsdisclosed herein and that various modifications, changes, and variationsmay be apparent from the foregoing descriptions without departing fromthe spirit and scope of the invention as defined in the appended claims.

What is claimed is:
 1. A single channel full duplex wirelesscommunication system, comprising: a processor; a transmitter coupled tothe processor, the transmitter transmitting a transmission signal via atransmission path; a receiver coupled to the processor, the receiverreceiving a received signal via a reception path, wherein thetransmitter and the receiver utilize one channel, at the same time, totransmit and receive said transmission and received signals with noseparation between frequencies used for the transmitting and thereceiving, wherein a portion of the transmission signal is leaked, saidleakage causing self-interference in the received signal; a secondarytransmission path coupled to the processor; and the processor estimatinga first transfer function, wherein the first transfer function has aninput comprising the transmission signal fed to the input of thetransmission path, and an output comprising the input adjusted by thefirst transfer function in such a way so as to reduce theself-interference in the received signal, and feeding the input of thesecondary transmission path with the output from the first transferfunction; a combining element connected to the input of the receiver andto the output of the secondary transmission path, to combine thereceived signal with the output from the secondary transmission path,thereby removing at least a fraction of the self-interference; and atransmission feedback path and a secondary transmission feedback path,wherein the input to the transmission feedback path is connected to theoutput of the transmission path, and the input to the secondarytransmission feedback path is connected to the output of the secondarytransmission path, the transmission feedback path output being modifiedby a second transfer function and the secondary transmission feedbackpath output being modified by a third transfer function, such thatcombining of the modified transmission feedback path output and themodified secondary transmission feedback path output with the receptionpath output reduces the remaining fraction of the self-interference. 2.The system of claim 1, wherein the combining of the modifiedtransmission feedback path output and the modified secondarytransmission feedback path output with the reception path outputproduces a recovered signal with an acceptable signal-to-interferenceratio.
 3. The system of claim 2, wherein the first, second and thirdtransfer function is implemented within the processor.
 4. The system ofclaim 3, wherein at least one of the first, second or third transferfunctions is nonlinear.
 5. The system of claim 4, wherein thetransmitter and the receiver utilize one antenna to transmit and receivesignals, the antenna being coupled to both the transmitter and thereceiver via a circulator-like device, said circulator-like deviceachieving a sufficient range of isolation through use of passive noisecancellation techniques, or active noise cancellation techniques, or anycombination thereof.
 6. The system of claim 4, further comprising afirst antenna and a second antenna, wherein the first antenna is atransmission antenna coupled to the transmitter and the second antennais a receiver antenna coupled to the receiver.
 7. The system of claim 4,comprising multiple transmission paths and multiple reception paths. 8.A method of improving signal-to-interference ratio in a single channelfull duplex wireless communication system, comprising: transmitting atransmission signal via a transmission path; receiving, by a receiver, areceived signal via a reception path, the transmission path and thereception path utilizing one channel, at the same time, to transmit andreceive transmission and received signals, with no separation betweenfrequencies used for the transmitting and the receiving, wherein aportion of the transmission signal is leaked, said leakage causingself-interference in the received signal; estimating, by a processor, afirst transfer function, wherein the first transfer function has aninput comprising the transmission signal fed to the input of thetransmission path, and an output comprising the input adjusted by thefirst transfer function in such a way so as to reduce theself-interference in the received signal; feeding, by the processor, theinput of a secondary transmission path with the output from the firsttransfer function the secondary transmission path being coupled to theprocessor; combining, by a combining element coupled to the input of thereceiver and to the output of the secondary transmission path, thereceived signal with the output from the secondary transmission paththereby removing at least a fraction of the self-interference;estimating, by the processor, a second transfer function and a thirdtransfer function; modifying, by the processor, a transmission feedbackpath output signal with the second transfer function and a secondarytransmission feedback path output signal with the third transferfunction, wherein the input to the transmission feedback path isconnected to the output of the transmission path, and the input to thesecondary transmission feedback path is connected to the output of thesecondary transmission path; and adding, by the processor, of themodified transmission feedback path output and the modified secondarytransmission feedback path output to the reception path output, therebyreducing the remaining fraction of the self-interference.
 9. The methodof claim 8, wherein the adding of the modified transmission feedbackpath output and the modified secondary transmission feedback path outputto the reception path output produces a recovered signal with anacceptable signal-to-interference ratio; wherein the first, second andthird transfer functions are implemented within the processor; andwherein at least one of the first, second or third transfer functions isnonlinear.
 10. A single channel full duplex wireless communicationsystem, comprising: a processor; a transmitter coupled to the processor,the transmitter transmitting a transmission signal via a transmissionpath; wherein a portion of the transmission signal is leaked; a receivercoupled to the processor, the receiver receiving a received signal, thereceived signal including the leakage from the transmission signal, thereceiver including at least one combining element and at least onereception path, wherein the transmitter and the receiver utilize onechannel, at the same time, to transmit and receive said transmission andreceived signals with no separation between frequencies used for thetransmitting and the receiving, wherein the at least one combiningelement is coupled to an input of the receiver and wherein the at leastone reception path is coupled to an output of the receiver, wherein thereceiver produces an output signal, the output signal includingself-interference caused by the leakage from the transmission signal; asecondary transmission path coupled to the processor and to thecombining element; and the processor estimating a first transferfunction, wherein the first transfer function has an input comprisingthe transmission signal fed to the input of the transmission path, andwherein the output of the first transfer function is fed to an input ofthe secondary transmission path to produce a first intermediate signalat an output of the secondary transmission path, wherein a firstcancellation signal is obtained based upon the first intermediatesignal, the first cancellation signal being subsequently combined withthe received signal in the at least one combining element so as toreduce the self-interference in the output signal from the receiver; asecond cancellation signal being generated by modifying a secondintermediate signal using a second transfer function, the secondtransfer function being estimated by the processor, the secondintermediate signal being obtained based on at least one of thetransmission signal or the first intermediate signal, the secondcancellation signal being subsequently combined with the output signalfrom the receiver within the processor, thereby further reducing theself-interference in the output signal from the receiver.
 11. The systemof claim 10, wherein the combining of the second cancellation signalwith the output signal from the receiver produces a recovered signalwith an acceptable signal-to-interference ratio.
 12. The system of claim11, further comprising: a transmission feedback path coupled to thetransmission path, wherein the input to the transmission feedback pathis connected to the output of the transmission path; a thirdcancellation signal, the third cancellation signal being generated fromthe transmission signal by directing a portion of the transmissionsignal output from the transmission path through the transmissionfeedback path and subsequently modifying the output of the transmissionfeedback path using a third transfer function, the processor estimatingthe third transfer function; the third cancellation signal beingsubsequently combined with the output signal from the receiver withinthe processor, thereby further reducing the self-interference in thereceiver output signal.
 13. The method of claim 12, further wherein thesecond intermediate signal is obtained by passing a portion of the firstintermediate signal through a secondary transmission feedback path,wherein the input of the secondary transmission feedback path isconnected to the output of the secondary transmission path.
 14. Thesystem of claim 13, wherein the at least one reception path comprises aplurality of stages; there are multiple secondary transmission paths,each secondary transmission path coupled to the transmitter and to acorresponding combining element, each corresponding combining elementcoupled to a corresponding input of one of the plurality of stages;wherein the output from the first transfer function is fed to an inputof each secondary transmission path to produce a corresponding firstintermediate signal at an output of each secondary transmission path,each corresponding first intermediate signal used to generate acorresponding first cancellation signal; and each corresponding firstcancellation signal combined with the received signal input to eachstage of the at least one reception path in the corresponding combiningelement, so as to reduce the self-interference in the output signal fromthe receiver.
 15. The system of claim 10, wherein at least one of thefirst, second or third transfer functions is nonlinear.
 16. The systemof claim 15, wherein the transmitter and the receiver are coupled to oneantenna to transmit and receive signals, the antenna being coupled toboth the transmitter and the receiver via a circulator-like device thatisolates the transmission signal from the received signal through use ofpassive noise cancellation techniques, or active noise cancellationtechniques, or any combination thereof.
 17. The system of claim 15,further comprising a first antenna and a second antenna, wherein thefirst antenna is a transmission antenna, the transmission antenna beingcoupled to the transmission path and wherein the second antenna is areceiver antenna, the receiver antenna being coupled to the receiver.18. The system of claim 15, wherein the nonlinear transfer function isimplemented based on a weighted sum of terms derived from the input tothe nonlinear transfer function by adding delays and applying a Taylorseries expansion.
 19. The system of claim 13, wherein the transferfunctions are linear, the processor estimates said transfer functionsbased on an adaptive filtering technique, and the adaptive filteringtechnique is based on a Wiener filter.
 20. The system of claim 19,wherein the transmitter and the receiver are coupled to one antenna totransmit and receive signals, the antenna being coupled to both thetransmitter and the receiver via a circulator-like device that isolatesthe transmission signal from the received signal through use of passivenoise cancellation techniques, or active noise cancellation techniques,or any combination thereof.
 21. The system of claim 19, furthercomprising a first antenna and a second antenna, wherein the firstantenna is a transmission antenna, the transmission antenna beingcoupled to the transmission path and wherein the second antenna is areceiver antenna, the receiver antenna being coupled to the receiver.22. A method of reducing self-interference caused by one or moretransmission signals in a single channel full duplex wirelesscommunication apparatus, comprising the steps of: transmitting one ormore transmission signals using a transmitter, the transmittingoccurring via one or more transmission paths coupled to the transmitter,wherein one or more portions of the one or more transmission signals areleaked; receiving one or more received signals using a receiver, the oneor more received signals including leakage from the one or moretransmission signals, the receiver comprising one or more combiningelements and one or more reception paths, wherein at least one combiningelement is coupled to an input of the receiver, wherein the receiverproduces one or more output signals, the one or more output signalsincluding self-interference, the self-interference being caused by theleakage from the one or more transmission signals; wherein thetransmitter and the receiver utilize one channel, at the same time, totransmit and receive said transmission and received signals with noseparation between frequencies used for the transmitting and thereceiving; generating one or more first cancellation signals; thegenerating of one or more first cancellation signals further including:estimating, by a processor, a first transfer function, wherein the firsttransfer function has one or more inputs comprising one or moretransmission signals fed to the inputs of the one or more transmissionpaths, feeding, by the processor, one or more secondary transmissionpaths with the one or more outputs from the first transfer function toproduce one or more first intermediate signals at one or more outputs ofthe one or more secondary transmission paths, each one of the one ormore secondary transmission paths being connected to the processor andto the one or more combining elements of the receiver; obtaining the oneor more first cancellation signals from the one or more firstintermediate signals; combining, using the one or more combiningelements within the receiver, the one or more received signals with theone or more first cancellation signals in the one or more combiningelements of the receiver, thereby reducing the self-interference in theone or more output signals; generating one or more second cancellationsignals; the generating of one or more second cancellation signalsfurther including: estimating a second transfer function, the secondtransfer function being estimated by a processor; generating one or moresecond intermediate signals using one or more secondary transmissionfeedback path output signals, wherein inputs to the one or moresecondary transmission feedback paths are connected to the outputs ofthe one or more secondary transmission paths; and modifying the one ormore second intermediate signals with the second transfer function toobtain the one or more second cancellation signals; combining, in theprocessor, the one or more second cancellation signals with the one ormore output signals from the receiver, thereby further reducing theself-interference in the one or more output signals; and wherein thefirst and second transfer functions are matrices of transfer functions.23. The method of claim 22, further comprising generating one or morethird cancellation signals, the generating of the one or more thirdcancellation signals further comprising: estimating a third transferfunction; the third transfer function being estimated by the processor,wherein the third transfer function is a matrix of transfer functions;modifying one or more transmission feedback path output signals with thethird transfer function; wherein inputs to the one or more transmissionfeedback paths are coupled to the outputs of the one or moretransmission paths; and adding the one or more third cancellationsignals to the one or more second cancellations signals and the one ormore output signals from the receiver, thereby further reducing theself-interference caused by the leakage from the one or moretransmission signals.
 24. The method of claim 23, wherein the adding ofthe one or more third cancellation signals to the one or more secondcancellations signals and the one or more output signals from thereceiver produces a recovered signal with an acceptablesignal-to-interference ratio.
 25. The method of claim 24, wherein atleast one of the one or more reception paths includes a plurality ofstages, wherein the inputs to at least some of the stages are coupled tocombining elements, and for each stage input coupled to a combiningelement, combining the input signal to the stage with a correspondingfirst cancellation signal in the combining element, thereby reducing theself-interference in the receiver output signal caused by the leakagefrom the one or more transmission signals.
 26. The method of claim 24,wherein at least one of the first, second or third transfer functions isnon-linear.
 27. The method of claim 26, wherein the nonlinear transferfunction is implemented based on a weighted sum of terms derived fromthe input to the nonlinear transfer function by adding delays andapplying a Taylor series expansion.
 28. The method of claim 27,including only one transmission path and only one reception path, thetransmitter and the receiver utilizing only one antenna to transmit andreceive signals, the antenna being coupled to both the transmitter andthe receiver via a circulator-like device isolating the transmit signalsfrom the receive signals through use of passive noise cancellationtechniques, or active noise cancellation techniques, or any combinationthereof.
 29. The method of claim 27, further comprising one or morefirst antennas and one or more second antennas, wherein the one or morefirst antennas are transmission antennas, the transmission antennasbeing coupled to the one or more transmission paths and wherein the oneor more second antennas are receiver antennas, the receiver antennasbeing coupled to the receiver.
 30. The method of claim 24, wherein thetransfer functions are linear, the processor estimates said transferfunctions based on an adaptive filtering technique, and the adaptivefiltering technique is based on a Wiener filter.